Mesenchymal stem cells refer to primitive cells that are able to differentiate into bone, cartilage, adipose tissue, nerve and muscle, etc., and are known as being contained in a large amount in bone marrow. In fact, mesenchymal stem cells are presently isolated from bone marrow and then studied for certain purposes or widely used in clinical trials for a variety of diseases.
Although it is easy to obtain mesenchymal stem cells from bone marrow, there are difficulties in acquiring bone marrow. Further, it is also difficult to solve the problems associated with an immune rejection reaction occurring when implanting stem cells to others.
Meanwhile, it is relatively easy to obtain umbilical cord blood compared with obtaining bone marrow, and also, where great numbers of umbilical cord blood units are secured, it is possible to employ umbilical cord blood stem cells that are identical with or most similar to histocompatibility genes of patients and thereby it is possible to solve the problems associated with immune rejection. However, it is relatively difficult to obtain mesenchymal stem cells from umbilical cord blood, compared with obtaining them from bone marrow and thereby there is difficulty in study and clinical applications.
Conventionally, there has been largely used a method of separating and culturing mesenchymal stem cells from umbilical cord blood within 24 hours from birth, using a density gradient centrifugation method. However, when the density gradient centrifugation method is applied to cryopreserved umbilical cord blood, it is difficult to separate cells and easy to lose cells, which makes it more difficult to culture mesenchymal stem cells that are present in umbilical cord blood in a minute amounts.
As conventional methods of isolating and culturing mesenchymal stem cells, reference is made to U.S. Pat. Nos. 5,197,985 and 5,486,359, which disclose a method of proliferating mesenchymal stem cells in isolating and culturing mesenchymal stem cells from human bone marrow. That is, U.S. Pat. No. 5,197,985 is directed to a method for inducing human bone marrow-derived mesenchymal stem cells to differentiate into bone-forming cells, comprising: providing human bone marrow-derived mesenchymal stem cells that have been isolated, purified and culturally expanded from a bone marrow specimen by adding the bone marrow specimen to a medium which contains factors which stimulate mesenchymal cell growth without differentiation and allows, when cultured, for selective adherence of only the mesenchymal stem cells to a substrate surface; applying the isolated, purified and culturally expanded human bone marrow-derived mesenchymal stem cells to a porous carrier; and, implanting the porous carrier containing the culturally expanded human bone marrow-derived mesenchymal stem cells into an environment containing factors necessary for differentiating the human mesenchymal stem cells into bone cells. In the method, the porous carrier comprises hydroxyapatite and tricalcium phosphate and the medium is comprised of BGJb medium with fetal bovine serum (FBS) or is comprised of F-12 Nutrient Mixture. Further, U.S. Pat. No. 5,486,359 discloses isolated human mesenchymal stem cells which can differentiate into cells of more than one tissue type (for example, bone, cartilage, muscle or marrow stroma), a method for isolating, purifying and culturally expanding human mesenchymal stem cells, and characterization and uses thereof, particularly research reagent, diagnostic and therapeutical uses of such cells. In the patent, mesenchymal stem cells are derived from bone marrow and cultured in BGJb medium containing fetal bovine serum.